Scattering Dark States in Multiresonant Concentric Plasmonic Nanorings

Plasmonic nanoantennas can feature a sophisticated spectral response that may be the springboard for a plethora of applications. Particularly, spectrally sharp Fano resonances have been at the focus of interest because of their promising applications in sensing. Usually, the observation of Fano resonances requires nanostructures that exhibit multiple plasmonic resonances such as higher-order multipole moments. We show that similar spectral features can be observed with nanoantennas sustaining solely electric-dipolar resonances. The considered nanoantennas consist of multiple concentric gold nanorings separated by thin dielectric spacers. These nanoantennas host multiple resonances with disparate line widths in the visible and near-infrared. We theoretically and experimentally show that the interference of these resonances causes Fano features and scattering dark states. The electric-dipolar character permits the use of a simplified dense-array theory to predict the response of arrays of such nanoantennas from the electric polarizability of the individual constituents. This paves the way for a simplified design of plasmonic metasurfaces.